In semiconductor device manufacturing, photolithography is typically used to transfer a pattern for forming semiconductor features onto the semiconductor wafer for the formation of multi-layered structures forming integrated circuits. During a photolithographic process, radiant energy having relatively small wavelengths such as ultraviolet light is passed through a mask also referred to as a reticle to expose a radiant energy sensitive material such as photoresist formed on the wafer process surface. The mask includes predetermined circuitry patterns having regions of attenuating and non-attenuating regions where the radiant energy intensity is modulated. For example, ultraviolet (UV) light passed through the mask onto the photoresist causes chemical reactions in the exposed portion of the photoresist altering it properties. Upon development of the photoresist exposed portions are removed in the case of a positive photoresist and non-exposed portions are removed in the case of a negative photoresist.
As semiconductor device feature sizes have decreased to sizes smaller than the wavelength of light used in photolithographic processes, the diffraction of light at feature pattern edges formed on the reticle causes a loss of resolution in transferring the reticle pattern to the wafer photoresist. To increase the resolution of photolithographic pattern transfer, phase shift masks have been developed where the phase of the wavefronts of light passing through alternating portions of the reticle pattern are shifted out of phase with respect to light passing through adjacent portions to produce destructively interfering wavefronts to reduce undesired exposure of the wafer photoresist due to diffraction of light at feature edges of the reticle pattern. As a result, the contrast, and therefore transferable resolution of the reticle pattern is improved.
There have been several different types of PSM's developed to improve resolution for different types of reticle patterns. For example, in an attenuated or halftone PSM, the phase shifting function is typically accomplished by adding an extra layer of transmissive material to the mask with predetermined optical properties. Some PSM's are designed to produce improved resolution while having little improvement in depth of focus, while other PSM's are designed to have a relatively modest increase in resolution while producing a greater improvement in depth of focus. For example, attenuated PSM's also referred to as halftone PSM's are of the latter type of PSM's.
Referring to FIG. 1A, for example, in one type of attenuated PSM, a halftone film 12 is formed over a fused silica substrate 10, also referred to as a quartz substrate. For example, the halftone layer 12 may be formed to transmit a portion of the light producing an accompanying phase shift. Formed overlying the halftone layer is an opaque layer 14 which is not transmissive to light.
Referring to FIG. 1B, a photoresist layer (not shown) is formed over the chromium containing layer and exposed with an E-beam tool or light source and developed to form a circuitry pattern, for example including lines, pads, and contact holes. The chromium containing layer and the halftone layer are subsequently etched to form a clear light transmissive area, for example opening 16, revealing the quartz substrate.
Still referring to FIG. 1B, one problem according to the prior art, is that during etching of the halftone layer 12, for example by a dry etching process, etching residues including halftone layer material,e.g., 18, frequently form along the sidewalls of the opening 16 thereby reducing the size of the opening. While a portion of the quartz substrate is frequently exposed at the bottom of the opening, for example, a contact hole, the opening is defective for transferring the contact hole pattern to a process wafer in a photolithographic process. Prior art processes have attempted to repair defectively etched openings by removing the residues in a subsequent process after removing the overlying chromium containing layer. The etching residues remaining within the opening have been removed by selectively dry etching the residues e.g., 18 surrounding the opening with, for example, a selective area etching tool using a series of masking processes around individually defective contact holes using, for example, XeF gas. However, the selective etching processes of the prior art are typically very time consuming and require expensive selective etching machines to selectively etch portions of the defective reticle pattern areas. Further, time consuming masking processes are required to avoid damage to the quartz substrate during the selective etching process and frequently result in damage to the quartz substrate. Another problem with prior art processes is the risk of shifting of the contact opening in the several alignment processes required to carry out the selective etching process, resulting in deviations from a critical dimension. As a result, the critical dimension of the a repaired opening must be verified following the selective etching repair process, further adding to the cycle time for a PSM repair process.
Thus, there is a need in the semiconductor device manufacturing art for a more reliable and cost effective method for repairing etching defects in the reticle patterning process to form attenuated phase shift masks.
It is therefore an object of the invention to provide a more reliable and cost effective method for repairing etching defects in the reticle patterning process to form attenuated phase shift masks while overcoming other shortcomings and deficiencies of the prior art.